1. Field of the Invention
This invention relates to dialysis machines, and more particularly to hemodialysis machines that have an extracorporeal blood circuit with a chamber that stores a quantity of blood.
2. Description of Related Art
Dialysis machines are used for treating patients with inadequate kidney function. Hemodialysis machines include, among other things, an extracorporeal blood circuit typically comprising an arterial line, a blood pump, a dialyzer and a venous line. Blood is removed from the patient via the arterial line and pumped by the blood pump to the dialyzer, where blood-borne toxins and excess fluids are removed from the patient's blood. The blood is then returned to the patient via the venous line.
Typically, extracorporeal circuits of hemodialysis machines include a blood drip chamber in the venous line which is designed to separate and remove bubbles of air or foam from the blood being returned to the patient. The chamber, sometimes referred to in the art as an "air trap", stores a quantity of blood which is constantly replenished by blood from the dialyzer, as blood is withdrawn from the chamber (typically from the bottom of the chamber) and returned to the patient. It is also common to have blood chambers in the arterial line leading to the dialyzer, especially in single needle dialysis systems.
During the course of the dialysis session, the blood level may rise above or fall below a predetermined or desired level in the chamber (e.g., the middle of the chamber), due to pressure changes in the extracorporeal circuit, changes in the pump rate of the blood pump, accidental occlusion at the blood access site and trapped air in the chamber displacing fluid. Problems can arise if the level goes too high or too low. For example, if the level in the drip chamber becomes too low, excessive foaming may occur or become entrained in the blood. If the level becomes too high, plasma may separate from whole blood and clotting may occur more readily.
In the prior art, adjustment of the level in an air trap was typically accomplished by manually operating valves or pumps that change the level of blood in the chamber, or by manually manipulating up and down buttons on the face of the dialysis machine which control the level adjustment apparatus. For example, the patent to Grogan et al., U.S. Pat. No. 5,326,476, which is incorporated by reference herein, incorporates up and down buttons on the face of the machine that control the operation of arterial and venous valves and a peristaltic pump. The user operates the buttons to raise or lower the level in the chamber.
It has also been proposed to use optical sensors to sense the level of blood chamber and a control system to responsively operate pressure adjustment apparatus to regulate the pressure and hence level in the chamber. See, e.g., the patent to Chevallet et al., U.S. Pat. No. 5,227,048, which is incorporated by reference herein.
The present invention departs from these approaches by using the user interface, and preferably a touch screen, as a way of indicating the current level of blood or other fluid in the air trap and using the central computer system to make adjustments to the level. Touch screen user interfaces are known in the dialysis art, see, for example, the above Grogan et al. patent. The Grogan et al. patent describes using the touch screen to select, enter and confirm certain parametric value changes for the machine. However, the Grogan et al. patent does not recognize the feasibility of using the touch screen to change the level of the drip chamber, and relies on the use of physical buttons on the face of the machine to control the blood chamber level adjustment apparatus.
Usage of the touch screen to adjust the level of a chamber in the extracorporeal circuit has several distinct advantages. First, it consolidates the user's interaction with the machine controls in one location. Second, it avoids the use of the optical sensors (such as described in the above Chevallet et al. patent), and thus is a less costly implementation since no additional hardware is required. Third, the usage of the touch screen and associated hard keys adjacent to the touch screen (described below) allows for backup safety and verification procedures to be implemented in the central computer control system for the machine, particularly where the user interface supplies input signals to a control system comprising host and backup safety central processing units, such as employed in the inventors' preferred embodiment of the invention.
These, and other advantages and features of the invention will become more apparent from the following detailed description of preferred and alternative embodiments of the invention.